Field of the Invention
The present invention relates to a diaphragm device for a video camera lens and a method for controlling the diaphragm device, and in particular, to a video camera lens capable of adjusting the amount of diaphragm by an actuator using a pulse signal driven motor.
Description of the Related Art
Imaging devices such as video cameras generally adopt a scheme in which a lens unit comprising a diaphragm mechanism is attached to a camera body.
Regarding such a diaphragm mechanism of the lens unit, a DC iris control mode and a video iris control mode are widely used as an automatic diaphragm control mode to automatically adjust and maintain the amount of light to an image sensor at an appropriate level.
The DC iris control mode and the video iris control mode have in common in that the diaphragm is automatically adjusted by an analog signal driven motor according to change in the luminance of a subject, but are different in that a control circuit is provided in the camera body in the DC iris control mode, whereas a control circuit is provided in the lens unit in the video iris control mode.
Therefore, it is required to use a camera body and a lens unit by appropriately combining them depending on their control modes. However, because a terminal structure between the camera body and the lens unit is common to the DC iris control mode and the video iris control mode, there have been cases where the camera body and the lens unit that are in conformity with different control modes incompatible with each other get connected.
Japanese Patent Application Laid-Open No. 2-030277 (hereinafter referred to as PTL 1) discloses an imaging device maintaining compatibility with both a lens that includes a built-in driving circuit for driving an optical diaphragm mechanism and a lens that does not include a built-in driving circuit. The imaging device of PTL 1 is provided with a second iris driving circuit independent of a first iris driving circuit, a first optical diaphragm mechanism is driven by the first iris driving circuit when a first lens is attached, and a second optical diaphragm mechanism is driven by the second iris driving circuit when a second lens is attached.
In addition, Japanese Patent Application Laid-Open No. 2001-320617 (hereinafter referred to as PTL 2) discloses an interchange connection device that enables use of lenses each including one of two different types of automatic diaphragm mechanisms by letting a user freely insert one of the lenses into a connector at a camera side and connect it with the connector regardless of the types. In the interchange connection device in PTL 2, switching an analog switch by detecting a change in voltage or current at each terminal of the connector enables coping with a VS control automatic diaphragm lens and a DC control automatic diaphragm lens.
On the other hand, nowadays, as a control mode other than the DC iris control mode and the video iris control mode, there have been also used video cameras adopting a so-called P-iris control mode that enables highly accurate control of the amount of diaphragm by a stepping motor.
In relation to the P-iris control mode, for example, Japanese Patent Application Laid-Open No. 2011-164614 (hereinafter referred to as PTL 3) proposes an approach that enables a camera side to use a parameter of a P-iris lens in a calibration method for a camera equipped with the P-iris lens.